Influence of resonant plasmonic nanoparticles on optically accessing the valley degree of freedom in 2D semiconductors
arxiv(2024)
摘要
The valley degree of freedom is one of the most intriguing properties of
atomically thin transition metal dichalcogenides. Together with the possibility
to address this degree of freedom by valley-contrasting optical selection
rules, it has the potential to enable a completely new class of future
electronic and optoelectronic devices. Resonant optical nanostructures emerge
as promising tools for controlling the valley degree of freedom at the
nanoscale. However, a critical understanding gap remains in how nanostructures
and their nearfields affect the polarization properties of valley-selective
chiral emission hindering further developments in this field. In order to
address this issue, our study delves into the experimental investigation of a
hybrid model system where valley-specific chiral emission from monolayer
molybdenum disulfide is interacting with a resonant plasmonic nanosphere.
Contrary to the intuition suggesting that a centrosymmetric nanoresonator
preserves the degree of circular polarization in the farfield, our cryogenic
photoluminescence microscopy reveals almost complete depolarization. We
rigorously study the nature of this phenomenon numerically considering the
monolayer-nanoparticle interaction at different levels including excitation and
emission. We find that the farfield degree of polarization strongly reduces in
the hybrid system when including excitons emitting from outside of the system's
symmetry point, which in combination with depolarisation at the excitation
level causes the observed effect. Our results highlight the importance of
considering spatially distributed chiral emitters for precise predictions of
polarization responses in these hybrid systems. This finding advances our
fundamental knowledge of the light-valley interactions at the nanoscale but
also unveils a serious impediment of the practical fabrication of resonant
valleytronic nanostructures.
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